Scientists are testing a sweet idea that might help organic cherry growers manage insects, birds, and diseases all in one go.
Organic growers have been successfully using the GF-120 protein bait to control the key pest, cherry fruit fly, but it does not provide sufficient control of the spotted wing drosophila, which has recently become a pest in the Pacific Northwest.
Dr. Alan Knight, entomologist with the U.S. Department of Agriculture in Yakima, Washington, said a number of conventional pesticides are available that will control spotted wing drosophila, but the only other product that organic growers can use is the pesticide Entrust (spinosad).
He has been researching a new bait consisting of sugar and yeast for managing spotted wing drosophila, which he thinks could benefit growers in multiple ways.
Dr. Wee Yee, also an entomologist with the USDA in Yakima, had discovered in his work with cherry fruit fly that adding sugar and yeast to insecticides made them more effective.
In tests, Knight and his colleagues found that adding the protein bait Nu-Lure to Entrust did little to enhance the performance of the pesticide. However, when he combined the pesticide with a sugar and yeast bait, more flies were killed and fewer eggs were laid.
They started out using brown sugar with a bread yeast and later found that white sugar worked well also. They went on to test many different types of yeasts, some isolated from fruit or insect bodies, and some purchased from catalogues.
Meanwhile, Knight learned that one grower in Yakima was reporting success using eight pounds of white cane sugar per acre on cherries to repel birds. The idea caught on, and 3,500 acres of cherries and Honeycrisp apples were treated last year. All the growers said it worked, Knight reported.
Knight decided to test the idea in a small trial at the USDA’s research orchard last season, making five weekly sprays of sugar. Treated trees had 1 percent fruit injury from birds compared with 4 percent in untreated trees. Knight said some birds, such as robins and starlings, lack a sucrase enzyme in their digestive system and eating cane sugar makes them sick, so they learn to avoid it. However, magpies were not deterred, he found.
Knight is continuing the sugar study this year and said if results continue to look promising, he will look at the possibility of combining the sugar with a yeast that has activity against fungal diseases, such as powdery mildew, brown rot, and botrytis fruit rot. The rate of yeast normally used for fungicidal purposes is 1.2 pounds per acre. Knight said he and his colleagues will evaluate what the ratios of the bait’s components should be with the goal of integrating the management of insects, diseases, and birds.